Phenotypic plasticity of the stem epidermis in the bluegrasses (Poa L.) of section Stenopoa Dumort. (Poaceae). I. Mesomorphic species

Section Stenopoa Dumort. is one of the largest representatives of the bluegrass genus (Poa L.). Despite relative antiquity, P. palustris L. and P. nemoralis L. have not been perserved in original states. Their ongoing evolution and hybridization has increased their diversity and has complicated the system. This obligate to search for new morphological characters, suitable for taxa discrimination, as well as for phylogenetic relationships. It is well known, that studying of grasses is difficult, bluegrass in particular. The reasons for this are next: their vegetative and reproductive organs structure is extremely uniform; the number of characters used in taxonomy is small as well as the number of these characters states. Meanwhile, characters of epidermis structure are widely used in the systematics and diagnostics of grasses. These characters consist of a presence or an absence of pubescence along the veins, lower lemmas keel and callus, and an rachilla. The main goal of the current work is to assess the variability of epidermis sculptural features, that determine the degree of stems and sheaths roughness of mesomorphic bluegrasses in Stenopoa section; and to assess the possibility of using these characters in taxonomy. Anatomical surfaces' study of stems and lower leaf sheaths was carried out with a Biolam-1 binocular light microscope (Russia) and a SEC SNE-4500M (SEM) scanning electron microscope (South Korea). Studies of diversity of stem and leaf epidermis structure on mass and serial herbarium materials showed that the change in the roughness degree has partly continual, partly discrete character. Sculptural formations are represented by a variety of crown cells, pricles, and bristles, that in fact are short stiff hairs. Thus, the characters of epidermis structure cannot be used as discriminators for mesomorphic bluegrasses of the Stenopoa section. These characters can act as additional ones and mark the evolutionary branches of P. palustris and P. nemoralis along with such morphological features as the length of the ligule and the rachilla pubescence.